Variation of valve actuation events in an automotive internal combustion engine provides improved low speed combustion processes and resultant system power output without sacrificing desired engine operating characteristics at high engine speed. Engines having pushrod actuated valve trains traditionally exhibit less flexibility with respect to valve train variability due to the location of the intake and exhaust valve actuators, or cam lobes, on a single crankshaft driven camshaft such as is illustrated in FIG. 1. In such an engine, a single rotating camshaft is typically located in the valley of the engine block above, and parallel to, the engine crankshaft. The camshaft actuates the intake and the exhaust valves via cam followers, pushrods and rocker arms. Because the inlet and exhaust valve events are fixed, relative to one another by placement of the inlet cam lobes 2 and exhaust cam lobes 4 on the same shaft, the timing or relationship of the events can not be easily altered.
A two-step cam follower is known, having two cylinders with a coincident longitudinal axis. The outer cylinder may be used for "high-lift" valve events and is operated on by a first pair of spaced cam lobes 6 of shaft 5' as is illustrated in FIG. 2, and the inner cylinder may be utilized for "low-lift" valve events and is acted on by a second cam lobe 7 between the first pair of lobes 6. As is evident from the illustrations of FIGS. 1 and 2, implementation of a two-step cam follower requires a greater investment in axial camshaft length, per valve, than in a non-variable system. In an internal combustion engine having a pushrod actuated valve train with specific, fixed cylinder bore center distances, the axial shaft distance between camshaft bearings may not permit the packaging of a two-step follower system.